The proposed research is designed to clarify the role of the basal ganglia and closely related nuclei in the planning, initiation and execution of limb and eye movements. We intend to study in these structures, in trained, behaving monkeys, (1) the relation of single cell activity to both the preparative and the executive aspects of motor behavior, and (2) the effects of electrical microstimulation and pharmacologic lesioning on these same aspects of limb and eye movements. The level of hierarchic control will be assessed by comparing the neural activity associated with combined eye and limb movements with the activity associated with eye movements alone. Similar comparisons will permit correlations of neural activity with the encoding and retention of spatial and temporal information about an intended movement. The functional properties of each neuron will also be characterized in terms of its response to perturbation and loading of the limbs during task performance, as well as its response to natural stimulation of cutaneous and deep structures outside of the task. Neural activity will be studied in the following structures: (1) striatum (2) globus pallidus, (3) substantia nigra, (4) nucleus basalis and (5) thalamus (nuclei ventralis anterior, ventralis lateralis). Analysis of the response properties of neurons at sequential points along the pathway from striatum-pallidum/s.nigra-thalamus-frontal cortex should reveal the operations performed at each successive stage. The effects of microstimulation and small lesions produced by the stereotaxic injection of kainic acid or 6-hydroxydopamine will be assessed with respect to executive and preparative motor functions. The results of these combined studies should provide insight into the pathophysiology of certain disorders affecting the basal ganglia, e.g., Huntington's disease and Parkinson's disease and clarify the role of the basal ganglia and related structures in normal motor function.